Using the various available manuals and
catalogs it is possible to construct a reference of Cat #'s (Catalog Numbers)
and Objectives that may be useful in finding objectives for your
AO Spencer microscope.

Description

Example Models

Time-frame

TL and parfocal distance

Metallurgical Scopes

Any era

Infinity TL

Black Scopes

Series 33, 35, etc.

1920s - 1956

160mm TL, 34mm parfocal*

The Blue-Gray Scopes

Series 1, 2, 4.

1956 until 1961

160mm TL, 34mm parfocal

The Gray Scopes, and Gray & White Scopes

Series 10, 20, 110, 120, etc.

1961 to 1985

Infinity, 34mm parfocal

The White Scopes

AO-Reichert, Reichert, Leica, Series 310, 410,
etc.

From 1985

Infinity, 45mm parfocal

The rules for objectives:

1. You cannot
put infinity corrected lenses on a 160mm TL scope, nor can you put 160mm TL
objectives on an infinity corrected scope . . . Yes, you'll get an image
sometimes . . . but not a very good one.

2. It is a pain to mix 34mm and
45mm parfocal objectives on the same nosepiece -- stick with one or the other --
or prepare to be frustrated and possibly to crunch an objective or two against
the slide and coverglass :-)

Eyepieces, on the other hand, are quite forgiving can be used interchangeably on 160mm TL and Infinity
corrected scopes with good results.*

*Note: The 'purist' in me wants to note that
the very best, optimum results will be obtained by using the eyepieces
specifically made for each objective set (e.g. a Cat# 146 10x
eyepiece on a 160mm TL Series 2 scope, a Cat# 176 10X eyepiece on an infinitely
corrected Series 10 scope, etc.) -- but the 'practical side' of me says it
really, truly doesn't make a heck of a lot of difference -- use what you have.
But if you are wondering what the differences might be between different brands
of eyepieces, Mervhob of Yahoo's Microscope Group has furnished the useful
information below (also see Mikrofibel
page 55) :

You can see that B&L
(Bausch & Lomb) eyepiece are very close to the same specifications as AO eyepieces.
It is quite common to
find B&L eyepieces on AO scopes and, probably, vice-versa. Amazingly,
you'll often find B&L objectives on AO scopes, without an shims, even though their parfocal
distance is 35.6mm vs. the 34mm distance for AO Objectives.

OK, Here is a list of the AO and Spencer
Objectives 'known' to me from either experience, or from the AO Spencer
Literature (i.e. a catalog or a manual). (Note: You can
select the whole list, top to bottom, and past it into Excel to create a
spreadsheet that can be sorted on any column if you'd like)

Sources:

#1 = 110 Objectives Catalog

#6 = AO 60 Manual

#11 = Series 2 & 4 Phase
Catalog

#16 - MetalStar 2200 manual

#2 = Series 10 Phase
Catalogs

#7 = AO 120 Manual

#12 = Series 10 Phase Manual

#17 - Seen on eBay

#3 = Epi Lume Catalog

#8 = 1969 Series 10 Manual

#13 = Series 15 & 35 Catalog

#18 -- AO PolStar Brochure

#4 = AO Starlight Catalog

#9 = eBay or have used one

#14 = Series 15 & 35 Phase
Catalog

#5 = BioStar Inverted Catalog

#10 = Series 2 & 4 Catalog

#15 = DN50, DN60 Dual View
Manual

Note: A 'C' at
the beginning of the Cat#, at least in the Series 15 and 35 era (1930's and
40's), meant 'C'oated. For example, you could order either a Cat#
115 uncoated 43x objective, or a Cat# C115 coated (Americote)
objective. A 'K' at the beginning of a Cat# designated a 'special
order' item.

*In the only case I know of, AO, strangely,
reused a Catalog number. In 1969, the Cat# 1029 was clearly a 50x (without
a iris diaphragm). Then sometime later AO brought out a Cat# 1029 100x Oil
( I've seen three examples of these -- they were 'new style' objectives so I
would guess the 1029 was maybe produced in 1975 or 1976?)

**Unsure if this whole number is the
Cat#. Only have seen on example of this objective, but this is what was on
it:

Stan Ayers -- "I just bought a
phase-contrast microscope. It seems to be from the '50's. The objectives and
condenser turret are familiar, except for one. There's a 50x reflecting
objective, marked 922968. I have never seen one of these, and was wondering what
they are for, or why they were specified."

Needham's 'Practical Use of the Microscope'
p.137: "A recent computation is that of the American Optical Company.
The reflecting objective is 50x with an N.A. of 0.56. The quartz optics
made by this Company for the objective are a 10x Huygens eyepiece and an Abbe
substage condenser." Read the full account here.

Answer: Sure . . . for almost 100 years, people have
been happily exchanging 160mm objectives But, there could be a few 'gotchas'.
First,
color and flatness correction sometimes occur in an intermediate lens (e.g. some
B&L designs) or, more commonly, in the eyepiece. But you have a good
chance of being successful without any loss of resolution and contrast.

Also,
remember the parfocal distance challenge. Sometimes, if the difference
isn't too great, you can use shims
between objective and nosepiece to defeat this challenge (e.g. see www.cynmar.com's
affordable parfocal rings).

A very useful table of parfocal distances is found in Mikrofibel
page 55 -- 1st column = Manufacturer, 2nd column = tubelength, and the 3rd
column = parfocal distance in mm -- which is what you need to know. Can't
read German? Me neither, but 'mining' this document we can produce a table
of good candidates as below:

FAQ Question:
Can I use other manufacturer's infinity corrected objectives with my infinity
corrected AO Objectives?

Answer: Not like you can 160mm objectives -- in
theory, many advise against it. But when did that ever stop you?
:-) After a rousing discussion on Yahoo's Microscope group about this (see
this message
for instance), and
reading various references, I have concluded (with not much authority I might
add :-) ) that it may work, or it may not work, depending on which
objectives and which scopes you use them on. A very good reference, and
read, is:

Basically, bottom line, even an infinity
system is designed with a tube-length in mind for the upper part of its optical
train, which varies by manufacturer, and the design 'mismatch' can cause trouble when
mixing various makes of infinity corrected objectives. (Note: A
interesting overview of objective correction can be found here.
The issue comes down to the question: "How can a single objective cost
$4000?", with the answer: "Because there's a lot to
correct for in attaining the ultimate resolution.")

But theory is one thing, practice is another. In
practice, people have found that it is often possible to swap infinity corrected
objectives without appreciable, or at least, noticeable, loss of resolution and
contrast. Remember though you will still face the parfocal distance
challenge mentioned above.

Answer: Sure. The Parfocal distance problem
will be there (i.e. many Leitz lenses are 45mm parfocal, some are 37mm parfocal,
etc.****), but it will
work. The definitive document on this is Leitz-160mm-Memo.pdf
at Gordon's site -- a very interesting read.

* Note: Determining the parfocal
distance of an AO objective is not as easy as it sounds -- well accurately at
least. I have two LOMO 160mm T.L. objectives which are very clearly stated
by the manufacturer to be 33mm parfocal. Using the 1 micron graduated fine
focus on the Series 4 scope, I found these LOMO objectives to be within 0.065mm
parfocal to each other. I then used them to compare against same power AO
160mm T.L objectives (which are within 0.040 mm parfocal to each other) and found the AO's parfocal distance to be almost exactly
1.0mm longer than the two LOMOs (0.925 mm in one case, 1.030 mm in the
other). So using the two Russian objectives as a standard (well, it was
the best I had), I compute the AO Objective's parfocal distance to be 34mm.

**Note: I compared an AO 97x Oil objective to a
B&L 97x Oil objective -- both gave excellent images (by the way, the 97x AO
was exactly parfocal with the 10x AO objective noted in the LOMO
comparison above). The B&L parfocal distance was exactly 1.67mm longer
than the AO's distance. Thus 34 + 1.67 = a 35.67mm parfocal distance for
B&L objectives. One
message on the Yahoo's Microscope forum says that B&L objectives are
35.5mm parfocal, but that is 0.17mm too short per my measurements.

***Note: Quoting from Needham (1958 -- The
Practical Use of the Microscope, p. 153): "American Optical Company
(Spencer) has designed objectives in which the central beam is not changed while
the diffracted light is both retarded and reduced in intensity. This
modification has been named by them, B minus contrast. American
Optical manufactures a very complete series of phase-contrast objectives for
bright, dark, and B minus contrast, each with three degrees of contrast of low,
medium, and high . . . The consensus of opinion of several of the foremost
independent workers with the phase-contrast microscope is that the Zernike, 1/4
(lambda) retardation, negative (bright) contrast or positive (dark) contrast is
preferred for the great majority of objects with very little contrast. Also
they object to the fact that too many variations in phase-contrast objectives
complicate and confuse the beginner in this field, and that such modifications
are not generally necessary, and that they add greatly to the cost."

****Note: Leitz objectives are a tough one to
unravel. Older Leitz objectives (before 1960?) seem to be all 37mm
parfocal. But when Leitz brought out PL (plan) and NPL (neo plan)
objectives, they designed them with the longer 45mm parfocal design.
But, unfortunately, it turns out to be no that simple. Note Mike Andre's
comment to a question about availability of 170mm T.L 37mm Phaco or PV
objectives -- Yahoo Microcope forum message #33059:

Looking at my copy of the Leitz manual
"Image-forming and Illuminating Systems of the Microscope"***** it states
on page 49: Phaco phase contrast objective for the Zernike condenser are
170/0.17/45mm
(with the exception of the Fl Oel 70 - 170/0.17/37mm)